The purpose of the present research is to identify and describe the effects of psychomotor stimulants, barbiturates, opiates and opiate antagonists on behavior and selected physiological systems in conscious nonhuman primates. Squirrel monkeys will be surgically prepared with chronically indwelling arterial and venous catheters for the direct measurement of blood pressure and intravenous administration of drugs. A wide range of doses of each drug will be administered acutely to determine the effects on systemic arterial blood pressure, heart rate and temperature. In other monkeys, the same drugs will be administered chronically to study the effects of chronic administration and, subsequently, termination of chronic administration on arterial blood pressure, heart rate and temperature. Other experiments in squirrel monkeys will study changes in psychological activity during ongoing behavior maintained by drug injection, food presentation or the postponement of electric shock and the effects of psychomotor stimulants, barbiturates, opiates and opiate antagonists in altering the behavioral and physiological activity. The research will provide definitive information on the way these classes of drugs affect blood pressure, heart rate, temperature and behavior, and the extent to which the effects can be blocked or antagonized.